There is a growing demand for manganese metal for use in the preparation in both ferrous and non-ferrous alloys. Furthermore, high purity manganese dioxide (MnO.sub.2) is a key component of long-life batteries. Both manganese metal and manganese dioxide are strong contendors as the media of transfer of stationary electrical power to electric vehicles. The cost of preparation of these materials is paramount for consideration in this application.
The conventional methods for preparing both manganese metal and manganese dioxide, each of high purity, is electro-deposition from a sulfate solution. Manganese dioxide is formed at the anode of an electrolyte cell and hydrogen is produced as a waste product. A cathode reaction produces manganese metal with oxygen as the waste product. Because of the significantly different operating conditions required for the production of these two materials, the reaction is carried out in two separate electrolytic cells and thus the electro-deposition of manganese metal and manganese dioxide are relatively expensive. If both products can be made in the same cell, electricity costs are cut approximately in half.
Studies have been made for producing two manganese products [Mn(OH).sub.2 and MnO.sub.2 ] in the same cell. This is described in the patent issued to N. V. Demuria, et al., U.S. Pat. No. 3,790,458, issued Feb. 5, 1974. According to this process, there is a saving in electricity; however, the current density is low and the cell structure is complex because membranes are required to physically separate two different electrolytes used for the production of these two manganese products. Demuria used sulfate electrolytes just as used in the production type of electrolytic cells described above.
Manganese dioxide is a by-product of certain other electrolytic processes. For example, it is a by-product of the electro-winning with zinc from purified zinc sulfate. The electro-deposition of manganese cannot be achieved in these systems with any high degree of current efficiency or current density because of the acid conditions in this sulfate media.
Another process for the production of manganese dioxide is disclosed in U.S. Pat. No. 3,770,868, issued to D. A. J. Swinkels, et al., on Nov. 6, 1973. This process involves the leaching of ores with hydrochloric acid in the presence of manganese chloride or magnesium chloride. This process does not utilize electro-deposition as in the other prior references cited above. The significant feature disclosed in this patent is that divalent manganese is oxidized by chlorine in low acid concentrations.
In other studies, the electro-deposition of manganese from sulfate, chloride, and mixed solutions has been conducted in electrolytic cells having a diaphram separating the anode and cathode regions. This work is reported by G. Parissis', et al., Paper No. A82-27 of The Metallurgical Society of AIME. It reports work performed in partial fulfillment in the requirements for a Ph.D degree. In general, it was found that higher current densities, current efficiencies, and overall power consumption per unit of production was achieved from chloride media.
As stated above, the cost of production of manganese metal and manganese dioxide is an essential factor, and for this reason high grade ores have been utilized for this purpose. However, essentially all of the high grade ores are exterior to the United States and therefore the ore (or products from the ore) must be imported. On the other hand, the United States has tremendous reserves of relatively low grade manganese ore which could be utilized if an efficient process was established. By low grade ore is meant ore that contains approximately ten (10) percent manganese. There is, for example, an extensive ore source that exists in a portion of the State of Maine which source extends into New Brunswick, Canada. This low grade ore is considered impractical for direct use in furnace steel products as compared to those from the higher grade feed stock from outside the United States. At the present time there has been no practical use of the low grade ore existing in the United States.
Accordingly, it is one object of the present invention to provide a process whereby ores containing on the order of ten (10) percent manganese can be utilized for the efficient production of manganese metal and manganese dioxide.
It is another object of the present invention to provide an electro-chemical process which utilizes the manganese from low grade ores in an electrolytic cell wherein high current densities and high current efficiencies are achieved to economically produce manganese and manganese dioxide.
It is a further object of the present invention to simultaneously electro-deposit, from a chloride media, manganese metal and manganese dioxide at the cathode and anode, respectfully, of an electrolytic cell having no partition between the anode and cathode compartments.
It is a further object of the present invention to develop an electro-deposition process for achieving high purity manganese metal and manganese dioxide from a chloride media by maintaining the hydrogen chloride within the electrolyte to a value less than about 0.1M.
These and other objects of the present invention will become more apparent upon a consideration of the accompanying drawings and the complete description of the invention as follow.